Draft hood



March 22, 1955 TUCK 2,704,538

DRAFT HOOD Filed Jan. 31, 1950 2 Sheets-Sheet 1 \NVENTOR fieorge ,4. 72x14 ATTORN EYS United States Patent DRAFT HOOD George A. Tuck, San Francisco, Calif., assignor to International Sales Company, San Francisco, Calif., a corporation of California Application January 31, 1950, Serial No. 141,365

3 Claims. (Cl. 126-307) This invention relates generally to draft hoods such as are employed with fuel gas burning appliances.

Draft hoods are commonly employed with heating appliances making use of natural gas or like fuel, and particularly gas-fired duct furnaces such as are used for domestic heating systems. The hoods are connected between the flue of the appliance and the chimney flue or other draft conduit employed to carry away the products of combustion. Such devices must comply with relatively rigid test standards. Thus in a normal installation blockage of the chimney flue or the outlet opening of the draft hood must not cause an increase in the concentration of carbon monoxide in the gaseous products of combustion beyond certain permissible limits. When a condition of downdraft occurs from the chimney flue into the draft hood, there must not be any detrimental effect upon the appliance, such as a serious increase in carbon monoxide concentration or extinguishment of the burner flame. In addition to these requirements, under normal draft conditions gaseous products of combustion should pass through the draft hood and into the chimney flue without escaping from the hood into the surrounding atmosphere.

Conventional draft hoods which have been used in the past have been relatively large and bulky, and particularly they have taken too much space for installation where the available space is restricted. As customarily installed the draft hood has extended for a considerable vertical dis tance above the top of the furnace, thus requiring excessive overhead space for a complete appliance installation. Many modern hot air heating furnaces are relatively small for their capacity, and in modern house constructions it is desirable to install them in closet or other spaces which are of limited vertical height. A draft hood made according to conventional designs greatly increases the space requirements of such compact furnaces, particularly with respect to the vertical height required, and thus the full economies of such appliances are not realized.

In general it is an object of the present invention to provide a draft hood which will overcome the difficulties of prior conventional devices of this character, and which will occupy a space of minimum height for its installation.

Another object of the invention is to provide a fuel appliance draft hood which is relatively compact with respect to its vertical dimensioning, and which obviates the necessity of maintaining a substantial vertical displacement between the openings of the hood which connect with the appliance and chimney flues.

Additional objects of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure 1 is a side elevational view in section illustrating a draft hood incorporating the present invention.

Figure 2 is a cross-sectional view taken along the line 2-2 of Figure 1.

Figure 3 is an enlarged detail illustrating the construction of the deflector elements.

Figure 4 is a side elevational view in section showing another embodiment of the invention in which the deflector elements are adjustable.

Figure 5 is a side elevational view in section, like Figure 1, but illustrating another embodiment of the invention.

Figure 6 is a cross-sectional view taken along the line 6-6 of Figure 5.

Figure 7 is a side elevational view in section illustrating another embodiment of the invention.

Figure 8 is a cross-sectional view taken along the line 88 of Figure 7.

The embodiment of the invention illustrated in Figures 1 to 3 consists of a housing 10 formed of suitable material such as sheet metal, and including the side walls 11, 12, 13 and 14, and the top wall 15. The lower end of this housing is open to the atmosphere as indicated at 16.

The side wall 11 has an opening 17 which is adapted to be connected with the flue 18 of the gas furnace or other appliance 19. The wall 13 is provided with the opening 20, adapted for connection with the laterally extending chimney flue pipe 21. It will be noted from Figure 1 that although the horizontal axis of the openings 17 and 29 are somewhat displaced in a vertical direction, the areas of these openings, when projected horizontally, are overlapping to a substantial extent. Interposed between the openings 17 and 20 there is flow control means designated generally at 22, and which serves to divide (i. e., segment) or break up flow of products of combustion through the hood to form a plurality of flow streams and which also serves as flow deflecting means.

In that form of the invention illustrated in Figures 1 to 3 the flow control means consists of a plurality of elongated deflector or bafile elements 23 made of suitable material such as sheet metal. In vertical section each element 23 as illustrated presents a curved concave face toward the opening 20, and. a curved convex face toward the opening 17. The curvature in this instance corresponds to a portion of a cylindrical surface. The adjacent elements 23 are spaced laterally and staggered to form the elongated spaced openings 24. It will be noted that these openings are arranged for generally vertical flow through the same. It is desirable for the elements 23 to be slightly tipped forwardly as illustrated in Figure 3, and likewise it is desirable that there be a slight overlap in a vertical direction between the adjacent upper and lower edges of the elements.

In the particular construction illustrated in Figures 1 to 3 the elements 23 are provided with tabs 26 at their ends which are secured by suitable means such as rivets or eyelets 27, to the mounting strips 28. These strips are in turn secured by suitable means to the side walls 12 and 14 of the housing.

It will be noted from Figures 1 and 2 that the elements 23 extend over an area which is somewhat greater than the horizontally projected area of opening 20. Therefore any horizontal flow occurring from opening 20 toward the flow control means 22 must impinge upon the elements 23, and cannot continue to flow directly into the opening 17. Also the extent of the flow control means 22 is such that the main flow of products of combustion in a horizontal direction from opening 17 into the housing must impinge upon the elements 23, although a minor portion may impinge upon that part of the wall 13 which extends below the outlet opening 20.

Operation of the draft hood described above can be explained as follows: Normally a continuous draft occurs through the chimney flue 21, to cause a continuous upward flow of air from the surrounding atmosphere through the bottom opening 16. A majority of the gaseous products of combustion leaving the gas appliance by way of flue 18 impinge upon the elements 23 and this flow is then divided (i. e. segmented) into a number of streams which proceed to flow through the openings 24. A minor part of the products of combustion may pass below the lowermost element 23, in flowing to the chimney flue 21. Air from the exterior atmosphere entering the lower end 16 of the hood commingles with the products of combustion before entering the chimney flue 21. Upward flow of atmospheric air through the bottom of the hood is sufficient under normal conditions to prevent any of the products of combustion from flowing downwardly and out into the atmosphere.

Assuming now that an abnormal downdraft occurs through the chimney flue 21, backflow from the opening 20 tends to occur in a horizontal direction to impinge upon the deflector elements 23. The elements deflect such flow to cause it to change direction, and ultimately the flow is spread laterally, segmented and directed downwardly through the elongated openings 24. Downward deflection of abnormal draft not only avoids creating a back pressure upon the appliance flue 18, but on the contrary tends to have an aspirating effect upon opening 17, whereby products of combustion under such abnormal conditions are delivered into the draft hood and are discharged through the lower opening 16. It will be evident from the foregoing that such abnormal conditions cannot interfere with proper combustion within the gas appliance, and it cannot cause such difiiculties as the extinguishment of the gas flame.

In the event the chimney flue 21, or the outlet opening 20 should be blocked, the products of combustion from the appliance find ready egress through the bottom opening 16 to the surrounding atmosphere, and this again occurs without imposing abnormal conditions on the appliance, such as might cause an increase in the carbon monoxide content beyond permissible limits.

The draft hood described above can be made to comply with all of the test requirements previously mentioned. A particular advantage is that the hood is relatively compact, particularly with respect to its vertical dimensioning. It will be noted that in Figure 1 the top of the hood is shown at the same level as the top of the appliance 19, and the chimney flue 21 extends laterally at a level below the top of the appliance. Such a draft hood is well adapted for very compact installations, as for example with compact types of domestic heating furnaces as previously described.

In the embodiment of the invention described above, the deflector elements 23 are stationary, and cannot be adjusted after assembly. As illustrated in Figure 4 it is possible to mount the deflector elements whereby they can be tilted to various selected angles after assembly. Thus in this instance small tabs 29 are attached to the ends of the deflector elements 23, and these tabs are pivotally attached at 31 to the side strips 28. The proectmg ends of all of the tabs 29 are shown attached to the operating rod or wire 33, whereby one can move this wire to change the angle of setting of all of the deflector elements. By the use of such an arrangement one can better adapt a draft hood to a particular gas appliance in order to insure proper operation. Thus for example by increasing the forward tilt of the deflector elements from that illustrated in Figure 3, one can increase the downward deflecting action under abnormal conditions when backflow occurs from the chimney flue.

In addition to the deflector elements 23, I can employ deflector elements extending in a general vertical direction, as illustrated in Figures and 6. Thus in this instance deflector elements 23 are employed the same as in Figure 1, together with supplemental deflector elements 36. Elements 36 are disposed on that side of elements 23 faced toward the outlet opening 20. It will be noted that elements 36 are in the form of strips which extend in a general vertical direction and which are inclined to the general direction of flow as illustrated in Figure 6. Such deflector elements 36 aid in spreading the flow laterally when abnormal backflow occurs through the outlet openmg 20. It will be evident that with this arrangement the deflector elements 23 may be either stationary as in Figure 1, or adjustable as in Figure 4. Likewise the strips 36 can be either stationary or adjustable to permit a change in the deflecting angle.

In place of the deflector elements previously described, I can utilize a louvre-like construction as shown in Figures 7 and 8 Thus a metal plate 38 is provided with struck out louvres 39 to provide the spaced elongated openings 41. These openings correspond generally to the openings 24 of Figures 1 to 3.

The sheet 38 is stiffened by the right angle flanges 42. The upper end portion 43 of the sheet may be seated in the corresponding corner of the housing, and the lower end portion is shown attached to the mounting bracket 44, which in turn is secured to the side walls 12 and 14. The width of the plate 38 is somewhat less than the lateral distance between walls 12 and 14, thus providing side passages 46.

The arrangement illustrated in Figures 7 and 8 likewise breaks up normal flow of products of combustion into a plurality of streams, as these gaseous products flow through the hood. In addition when an abnormal downdraft condition occurs, flow from the outlet opening 20 in a horizontal direction is not permitted to discharge directly into the opening 17, but is caused to be deflected and discharged downwardly through the openings 41 and from thence through the bottom hood opening 16. It will be noted that the side passages 46 cannot permit any direct flow from outlet opening 20 to the opening 17, because the lateral extent of the plate 38 is greater than the projected areas of these openings, as is apparent from Figure 8.

The novel flow control means incorporated in my draft hood is relatively simple in construction, and can be easily and economically manufactured from ordinary sheet metal. Such a draft hood can be made to serve satisfactorily with a wide variety of domestic furnace installations, although as previously explained it is particularly adapted in instances where space is an important factor.

I claim:

1. A draft hood for fuel gas heating appliances of the type having an appliance flue for discharge of gaseous products of combustion, a hood-like housing having a downwardly directed lower open end, a laterally directed inlet opening communicating through one side wall of the housing and adapted to make connection to the appliance flue, a laterally directed outlet opening communicating through the opposite side wall of the housing for making connection with a chimney flue, and flow control means within the housing and interposed between the inlet and outlet openings, said flow control means serving to divide normal flow of gaseous products of combustion from the inlet opening to the outlet opening into a plurality of upwardly directed adiacent flow streams, said last means occupying a general plane extending downwardly from a region adjacent the upper edge of the inlet opening to a region intermediate the lower edges of the inlet and outlet openings.

2. A draft hood for fuel gas heating appliances of the type having an appliance flue for discharge of gaseous products of combustion, a hood-like housing having a downwardly directed lower open end, laterally directed inlet opening in one vertical side wall of the housing and adapted to make connection to the appliance flue, a laterally directed outlet opening communicating through the opposite vertical side wall of the housing for making connection with a chimney flue. the areas of said openings when projected horizontally being overlapping to a substantial extent and the axis of the outlet opening being at an elevation above the axis of the inlet, and flow segmenting and deflecting means interposed between said openings, said means comprising a plurality of horizontally extending deflecting elements disposed in spaced relationship to provide flow openings between, said openings being formed to guide flow in a general vertical direction therethrough, said elements presenting deflecting surfaces to back flow of gas from the outlet opening to direct such back flow in a general downward direction and through the lower opening of the housing. said elements being grouped generally in a plane extending downwardly from a region adjacent the upper edge of the inlet opening to a region intermediate and spaced laterally from the lower edges of the inlet and outlet openings, there being a substantial unobstructed passage between the lower edge of said plane and the lower edge of said outlet opening.

3. A draft hood for fuel gas heating appliances of the type having an appliance flue for discharge of gaseous products of combustion, a hood-like housing having a downwardly directed lower open end, a laterally directed inlet opening in one vertical side wall of the housing and adapted to make connection to the appliance flue, a laterally directed outlet opening communicating through the opposite vertical side wall of the housing for making connection with a chimney flue, and flow segmenting and deflecting means interposed between said openings, said means comprising a plurality of deflecting elements disposed in spaced relationship to provide flow openings between the same, said openings being formed to guide flow from an initial horizontal to a general vertical direction therethrough, said elements as viewed in a horizontal direction from the outlet opening being vertically overlapping, and as viewed in plan being spaced, said elements presenting deflecting surfaces to back flow of gas from the outlet opening to direct such back flow from generally horizontal to a general downward direction through the lower opening of the housing, said elements being grouped generally in a plane inclined downwardly from a region adjacent the upper edge of the inlet opemng to a region intermediate and spaced laterally from the lower edges of the inlet and outlet openings, there being substantially unobstructed pas- 5 sages between the lowermost one of said elements and the lower edges of both the inlet and outlet openings, said lowermost element extending to a level below the lower edge of the outlet opening but being spaced a substantial vertical distance from the lower end of the housing.

References Cited in the file of this patent UNITED STATES PATENTS McCreery Dec. 29, 1896 Handley Nov. 26, 1940 Livar Sept. 30, 1941 Goerg Mar. 16, 1943 Coburn Oct. 3, 1944 FOREIGN PATENTS Great Britain Aug. 11, 1927 Great Britain Mar. 16, 1938 

